Embodiments of the present invention relate generally to a power flow in a power system. More specifically, the embodiments relate to damping of power system oscillations.
The power system is a complex network comprising of numerous generators, transmission lines, a variety of loads and transformers. With increasing power demand in the power system, some transmission lines are more stressed than was planned when they were built. Since stressed conditions can lead a system to unstable conditions, power system stability has become an important issue. In simple terms, power system stability is defined as the ability of the power system to return to a normal state after a disturbance. The disturbance may be a fault, a loss of a generator or even a sudden increase in power loading which results in power oscillations in power system.
Small signal stability is a power system stability issue related to low frequency oscillations between generator rotors. It has been the main reason for many power blackouts across the world including the Western Electricity Co-ordination Council (WECC) blackout of 1996. When the power system is heavily loaded, it often exhibits multi-mode oscillations because machine rotors, behaving as rigid bodies, oscillate with respect to one another using the electrical transmission lines between them to exchange energy. These oscillations generally lie in a frequency range between 0.1-3 Hz. The oscillations in this frequency range are generally analyzed in two main oscillation modes: 1) a local mode in the range of 1 to 3 Hz i.e., a generator or a group of generators in a plant swinging against the rest of the system and 2) an inter area mode in the range of 0.1 to 1 Hz i.e., machines in one group oscillate against machines in another group.
To stabilize the power system, damping measures to damp the power oscillations are utilized. Power system stabilizers (PSSs) are the most common damping control devices in power systems. Apart from PSSs, power oscillation damping (POD) can be effectively achieved through supplementary control of Flexible AC Transmission Systems (FACTS) devices installed in key transmission corridors. Traditionally, classical control theory has been adopted for design of such controllers which require an accurate model of the system at a particular (nominal) operating condition. However, lack of availability of accurate and updated information about each and every dynamic component of a large inter-connected system and its ever changing nature often puts a fundamental challenge on such model based approaches. Indirect adaptive controllers, which rely solely on system measurements, are useful for power system stabilizers (PSS) and also for the FACTS devices. These controllers are updated online based on the estimated model of the system and thus can adapt to the changes in operating conditions. However, present architectures of indirect adaptive controllers utilize complex multi-input multi-output (MIMO) structure. This leads to a multivariable controller, which is very complicated in nature.
For these and other reasons, there is a need for an improved indirect adaptive controller for power oscillation damping.